It has long been an object of silver halide-based color photographic materials to create an image of an object in an accurate manner, both in terms of color and image structure characteristics such as graininess and sharpness. It is well known that the perceived sharpness of photographic images can be degraded through halation effects; that is, the reflection and subsequent diffusion of light within the light capturing element; in particular, reflection from the support. It is well known to use antihalation layers between the support and the sensitized layers in films to reduce light reflection. To be effective, an antihalation layer contains materials that absorb light and prevent reflection. In general, it is highly desirable for the light absorbing materials to be totally removed from the film element (or otherwise made colorless) after development in order to avoid increased background density. One well known type of light absorbing material suitable for use in antihalation layers is colloidal or finely divided elemental or metallic silver (also referred to as `grey` silver). This type of silver metal is in a filamentary form and, is such form, absorbs light across the visible spectrum appearing grey or black. It is generally easily removed from the film element by the normal bleaching and fixing steps used to remove imaging silver from the element. This silver metal is not light sensitive and does not contribute to image formation. For references, see T. H. James, The Theory of the Photographic Process, 4.sup.th Edition, p. 579, U.S. Pat. No. 3,434,839, JP 09-067122A2 and Y. J. Zahng et al, Chin. Chem. Lett. 7(7), 687-690(1996).
Another use of colloidal or finely divided elemental or metallic silver is as a blue light absorbing filter. This form, commonly referred to as Carey-Lea silver, differs from `grey` silver by being spherical in form. For references, see F. Evva, J. Signalaufzeichnungmaterialien, 4(1), 43-60(1976) and G. Frens, Kolloid-Z.Z. Polym, 233(1-2), 922-9(1969). This material is generally located in a non-imaging layer (commonly referred to as a yellow filter layer) farther away from the exposing source than or "underneath" the blue light sensitive emulsion layer. The function of this layer is to absorb any blue light not captured by the blue sensitized layers, thus avoiding undesired exposure by blue light of the underlying green and red sensitized emulsion layers, which retain some inherent sensitivity to blue light.
A problem associated with the use of elemental silver in both antihalation and yellow filter layers is an undesired increase in fog in nearby imaging layers. During development, silver ions are released and/or made soluble from the imaging layer. These silver ions can migrate to a non-light sensitive layer where the elemental silver is present. The silver can serve as nuclei for the reduction of the migrating silver ions to silver metal with concurrent oxidation of developer to oxidized developer. This process is called solution physical development (for references, see T. H. James, ibid., Chapter 13) and is non-imagewise. The oxidized developer can diffuse out of the antihalation layer and back into the nearby imaging layer where it can react with the couplers present and form dye in a non-imagewise fashion. This process is often highly process sensitive and can lead to variations in Dmin during photofinishing.
Another problem with the use of elemental silver in non-imaging layers is that these layers can absorb inhibitor fragments and other silver absorbing materials. This results in lower effective concentrations of the free species in the imaging layers. Restricted diffusion of such species through the layer containing the elemental silver can also occur.
It is known that the solution physical development involving elemental silver can be modified by the use of additives. For example, GB 2280276 A1, DE 1949418, East German Patent 2006 91/6 and Japanese Patent Application (Kokai) JP 3-14 138639A2 all describe various classes of materials that are useful for controlling the properties of elemental silver. In particular, JP 6-347940 describes among others, the use of bentrotriazoles and other nitrogen heterocycles. However, in all of these references, the materials are water soluble and, of all the examples shown, the maximum ClogP is 3.79. Such water soluble materials can undesirably diffuse to imaging layers where they can cause inhibition of development and loss of sensitivity to light.
Solution physical development can be promoted by materials that form soluble silver salts. In particular, materials that release low molecular weight water solubilized thiols, which are used as bleach accelerators, can increase the amount of solution physical development. Couplers that release such thiols are known are bleach accelerator releasing couplers; for examples, see EP 193389, U.S. Pat. No. 4,861,701; U.S. Pat. No. 4,959,299; U.S. Pat. No. 4,912,024; U.S. Pat. No. 5,300,406 and U.S. Pat. No. 5,358,828. It is also possible to release the same bleach accelerators from materials other than couplers by imagewise means that do not involve direct coupling with oxidized developer; for example, see U.S. Pat. No. 4,684,604 or by non-imagewise means, for examples, see U.S. Pat. No. 4,923,784, U.S. Pat. No. 4,865,956 and U.S. Pat. No. 5,019,492. Thus, increases in Dmin in imaging layers near to non-imaging layers which contain collodial silver are particularly problematic when bleach accelerators are also present.
Substituted triazoles, including 1,2,3-triazoles, 1,2,4-triazoles (including tetraazaindenes) and benzotriazoles, are commonly known in the art as inhibitor fragments and as antifoggants; for example, as in U.S. Pat. No. 3,671,255. As inhibitor fragments, they are attached to a coupling moiety through a nitrogen atom and do not interact with silver until coupling occurs and the nitrogen atom is freed. As antifoggants, these materials are added directly to silver emulsions before coating of the film or added directly to the developer solutions. JP-60-29390 describes the use of ballasted benzotriazoles for use as inhibitor fragments attached to couplers to form Development Inhibitor Releasing Couplers (DIRs). U.S. Pat. Nos. 5,275,931; 4,920,043; and 4,720,451, and Japanese Patent Applications (Kokai) JP-63-193147, JP-60-217358, JP-59-159162, JP-57-125939, JP-4-204937, JP-1-137255 all describe the use of various triazole and benzotriazole derivatives for use as antifoggants. U.S. Pat. No. 5,508,154 describes the use of bicyclic heterocycles that contain a minimum of 4 nitrogen atoms as antifoggants in systems that contain inhibitor releasing couplers. DE 1 95 07913 A1 describes the use of ballasted benzimidiazoles to improve granularity particularly with certain pyrazolone image couplers. EP 0 369 486 B1 describes the use of various heterocyclic thiols with fine silver chloride emulsions to remove inhibiting species. U.S. Pat. No. 4,871,658 describes the use of tetrazoles with silver iodobromide emulsions to decrease fog. All of these materials are used for control of imaging silver halide emulsions in light sensitive layers and are not used in non-imaging layers.
U.S. Pat. No. 5,464,733 describes the use of an interlayer between an antihalation layer containing colloidal silver and imaging layers containing bleach accelerators to control Dmin. In general, the Dmin in any imaging layer directly adjacent to a layer containing elemental silver can be reduced by placing a non-silver containing interlayer between them. However, this adds to the overall number of layers present in the film and increases film thickness and manufacturing complexity.
One particular problem is high red Dmin whenever a red sensitized layer is directly adjacent to an antihalation layer that contains black colloidal silver. This is further aggravated whenever there are multiple red sensitized layers of different overall degree of light sensitivity present. However, multiple layers are desirable for reducing granularity through more effective use of silver centers. For this reason, the red record is commonly divided into either two layers of different red sensitivity (for example, see U.S. Pat. No. 5,464,733) or three layers (for example, see U.S. Pat. No. 4,886,738). In each of the above examples, an interlayer between the least sensitive (bottom-most) red record and the antihalation layer is used.
Improvements in granularity can be obtained by dividing a color record into four layers of different degree of light sensitivity, for example as described in JP 60-28652 and JP 60-03628. However, in this case, while dividing a red color record into four separate layers can allow for improved granularity, it adds to the number of layers that must be coated and is constrained by the additional need to have an interlayer between an antihalation layer containing elemental silver layer and the nearest imaging layer. This also applies to blue and green color records which can be adjacent to a non-imaging yellow filter layer which contains Carey-Lea silver.
A problem to be solved is to provide a photographic element containing a non-light sensitive layer containing elemental silver which has a reduced tendency to increase the Dmin of nearby light sensitive layers. An additional problem to be solved is to minimize the number of layers necessary in a photographic element to meet Dmin requirements, said element having non-imaging layers that contain elemental silver.